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"It hurt, but I wasn't all '911' about it. It was painful and swollen but I figured it would be okay without any medical intervention. Maybe a little bit of denial?" O'Brien wrote.

His arm seemed sore and swollen the next day, but didn't appear worse. That night, though, he experienced greater pain and swelling, and the next day asked the hotel where he was to refer him to a doctor.

Muscles in the arms and legs are separated from each other by thick layers of tissue called fascia, and each fascia has space in it, called a compartment, with muscle tissue, nerves and blood vessels.

When there is swelling in a compartment, pressure in that area will increase and press on the muscles, blood vessels and nerves.

"If this pressure is high enough, blood flow to the compartment will be blocked," according to the NIH's MedlinePlus resource. "This can lead to permanent injury to the muscle and nerves. If the pressure lasts long enough, the muscles may die and the arm or leg will not work any more. It may need to be amputated."

Symptoms of severe cases of compartment syndrome include skin paleness, numbness, tingling, decreased sensation, weakness and severe worsening pain. Early diagnosis and treatment are key for a good recovery.

Patients need immediate surgery, which involves making long cuts through the muscle tissue to relieve pressure. O'Brien's doctor recommended this procedure, also known as a fasciotomy.

After entering surgery, O'Brien woke up to learn that his blood pressure had dropped during the procedure. To save him, the doctor had made the decision to amputate just above the elbow.

"He later told me it all boiled down to a choice...between a life and a limb," O'Brien wrote.

Since then, O'Brien has dealt with "phantom pain, the vicissitudes of daily life with one hand and the worries about what lies ahead," he wrote.

But he says he is grateful to be alive and urged readers not to worry.

O'Brien, who covered the U.S. space program for CNN, currently lives in Washington and focuses on science, technology and aerospace in his journalistic work, which includes being the science correspondent for PBS NewsHour. His website says he frequently pilots his own airplane to assignments.

He ended his blog post poignantly: "Life is all about playing the hand that is dealt you. Actually, I would love somebody to deal me another hand right about now -- in more ways than one."